So I had the idea of spraying some nitrous on the track just to cool down the air temp going to the engine, but I was not sure as to what size jet to use. After talking too several guys here, they recommended a 25 shot which I think it's fine.

Now, I decided to buy the parts separately instead of buying the whole kit, which I think I could save a few hundred bucks here and there.

you want the micro switch. If im correct then that is what senses wide open throttle. You can put a push button on the positive wire and then make it so it is push button only. I dont recommend it though. I would think tuning would be a little harder since you never know when your going to hit it.